Final answer:
Pulmonary hypoplasia is most commonly caused by diaphragmatic hernia.
Step-by-step explanation:
Pulmonary hypoplasia is most commonly caused by diaphragmatic hernia. Diaphragmatic hernia is a congenital condition in which there is a hole in the diaphragm, allowing organs from the abdomen to move into the chest cavity. This can compress the lungs and prevent them from developing properly.
Other causes of pulmonary hypoplasia include oligohydramnios, a condition characterized by low levels of amniotic fluid, which can restrict the growth of the lungs, and pulmonary agenesis, a rare condition in which one or both lungs fail to develop.